Secondary DC resistance

What is a typical value of DC resistance of secondary winding of a small stepdown mains transformer used in some cheap Chinese power supplies. I couldn't find any datasheets. This the transformer is 240V to 12V and after bridge and smoothing caps, the max load is 500mA.

To provide .5 amps, ohmic resistance must not be higher than 12/.5 (=24) ohms.

Even if it is 24 ohms or less, it's no guarantee you'll get .5 amps of pure sinewave from it.

Just how much it will give you depends on a few other factors such as resistance in the primary windings, metal mass, saturation point, etc.

What AC voltage do you get with nothing attached? (Let's say you get 12V).

Then attach diodes and caps. With no load. Does voltage rise to 16 V or so? This is normal.

Once you start attaching a load, however much it drops is what you get.